ZyXEL Communications P-312 manual Types of DoS attacks, Common IP Ports

P312 Broadband Security Gateway

	Table 13-1		Common IP Ports
21	FTP	53	DNS
23	Telnet	80	HTTP
25	SMTP	110	POP3

13.3.2 Types of DoS attacks

There are four types of DoS attacks:

1.Those that exploit bugs in a TCP/IP implementation.

2.Those that exploit weaknesses in the TCP/IP specification.

3.Brute-force attacks that flood a network with useless data.

4.IP Spoofing.

1."Ping of Death" and "Teardrop" attacks exploit bugs in the TCP/IP implementations of various computer and host systems.

1-aPing of Death uses a "ping" utility to create an IP packet that exceeds the maximum 65,536 bytes of data allowed by the IP specification. The oversize packet is then sent to an unsuspecting system. Systems may crash, hang, or reboot.

1-bTeardrop attack exploits weaknesses in the reassembly of IP packet fragments. As data is transmitted through a network, IP packets are often broken up into smaller chunks. Each fragment looks like the original IP packet except that it contains an offset field that says, for instance, "This fragment is carrying bytes 200 through 400 of the original (non fragmented) IP packet." The Teardrop program creates a series of IP fragments with overlapping offset fields. When these fragments are reassembled at the destination, some systems will crash, hang, or reboot.

2.Weaknesses in the TCP/IP specification leave it open to "SYN Flood" and "LAND" attacks. These attacks are executed during the handshake that initiates a communication session between two applications.

Figure 13-2 Three-Way Handshake

13-4 What Is a Firewall?